Detroit’s dirty petcoke piles disappear, but where did they go?

The Koch brothers finally took their towering piles of tar-sands oil refinery waste away from Detroit.

But where did they send the stuff? That’s a bit of a mystery.

Huge piles of petroleum coke started building up along the city’s riverfront after a refinery began processing tar-sands oil from Canada in November. Koch Carbon, an affiliate of Koch Industries, peered into the dark mass and saw, ka-ching, opportunity, so it bought up all the waste.

The material has little commercial value in the U.S., where burning it would likely violate clean air laws unless expensive emissions-control equipment were used. But it can be sold for a decent-enough price in other countries with laxer air pollution laws. Indeed, we told you in June that ships were hauling some of the waste back to a power plant in Canada — but not enough of it to keep the piles from growing.